Use handles instead of self-pointers

axl_memory.c

@@ -2,18 +2,31 @@
 
 static u8 memory[AXL_HEAP_SIZE];
 
+#if AXL_HEAP_SIZE <= 0xFF - 1
+typedef u8 mb_handle;
+#define AXL_INVALID_MB_HANDLE 0xFF
+#elif AXL_HEAP_SIZE <= 0xFFFF - 1
+typedef u16 mb_handle;
+#define AXL_INVALID_MB_HANDLE 0xFFFF
+#elif AXL_HEAP_SIZE <= 0xFFFFFFFF - 1
+typedef u32 mb_handle;
+#define AXL_INVALID_MB_HANDLE 0xFFFFFFFF
+#else
+#error UNSUPPORTED HEAP SIZE
+#endif
+
 typedef struct mb_header mb_header;
 
 struct mb_header
 {
     u32 size;
     b8 is_free;
-    mb_header* prev;
+    mb_handle prev;
-    mb_header* next;
+    mb_handle next;
 };
 
-static mb_header* root = NULL;
+static mb_handle root_handle = 0;
-static mb_header* nomad = NULL;
+static mb_handle nomad_handle = 0;
 
 #define AXL_ALIGNMENT 8
 
@@ -22,6 +35,21 @@ static inline u32 axl_align(u32 size)
     return (size + (AXL_ALIGNMENT - 1)) & ~(AXL_ALIGNMENT - 1);
 }
 
+static mb_header* axl_id_to_mb(mb_handle id)
+{
+    if(id == AXL_INVALID_MB_HANDLE)
+    {
+        return NULL;
+    }
+
+    return (mb_header*)&memory[id];
+}
+
+static mb_handle axl_ptr_to_id(mb_header* ptr)
+{
+    return (mb_handle)((u8*)ptr - memory);
+}
+
 #define MB_HEADER_SIZE axl_align(sizeof(mb_header))
 
 void* axl_memset(void* ptr, i8 c, u32 n)
@@ -44,23 +72,23 @@ void axl_init(void)
     if(!axl_initialized)
     {
         axl_memset(memory, 0, AXL_HEAP_SIZE);
-        root = (mb_header*)memory;
+        mb_header* root = axl_id_to_mb(root_handle);
         root->is_free = true;
-        root->next = NULL;
+        root->next = AXL_INVALID_MB_HANDLE;
-        root->prev = NULL;
+        root->prev = AXL_INVALID_MB_HANDLE;
-        root->size = AXL_HEAP_SIZE - MB_HEADER_SIZE; 
+        root->size = AXL_HEAP_SIZE - MB_HEADER_SIZE;
         axl_initialized = true;
     }
 }
 
-static inline mb_header* axl_get_mb_header(void* ptr)
+static inline mb_header* axl_ptr_to_mb(void* ptr)
 {
     return (mb_header*)((u8*)ptr - MB_HEADER_SIZE);
 }
 
 static mb_header* axl_find_mb(u32 req_size)
 {
-    mb_header* block = nomad ? nomad : root; 
+    mb_header* block = nomad_handle ? axl_id_to_mb(nomad_handle) : axl_id_to_mb(root_handle); 
     mb_header* start = block;
 
     while(block)
@@ -70,12 +98,12 @@ static mb_header* axl_find_mb(u32 req_size)
             return block;
         }
         
-        block = block->next;
+        block = axl_id_to_mb(block->next);
 
         if(!block)
         {
             //nomad pointer didn't help us, start from root
-            block = root;
+            block = axl_id_to_mb(root_handle);
         }
 
         if(block == start)
@@ -98,15 +126,15 @@ static b8 axl_split_mb(mb_header* block, u32 size)
             new_block->size = block->size - size - MB_HEADER_SIZE;
             new_block->is_free = true; 
             new_block->next = block->next;
-            new_block->prev = block;
+            new_block->prev = axl_ptr_to_id(block);
 
             if(new_block->next)
             {
-                new_block->next->prev = new_block;
+                axl_id_to_mb(new_block->next)->prev = axl_ptr_to_id(new_block);
             }
 
             block->size = size; 
-            block->next = new_block;
+            block->next = axl_ptr_to_id(new_block);
 
             return true;
         }
@@ -139,10 +167,10 @@ void* axl_malloc(u32 size)
     axl_split_mb(free_block, size);
     free_block->is_free = false;
 
-    nomad = free_block->next;
+    nomad_handle = free_block->next;
-    if(!nomad) 
+    if(nomad_handle == AXL_INVALID_MB_HANDLE) 
     {
-        nomad = root;
+        nomad_handle = 0;
     }
     
     return (void*)((u8*)free_block + MB_HEADER_SIZE);
@@ -173,7 +201,7 @@ void* axl_realloc(void* ptr, u32 size)
         return axl_malloc(size);
     }
 
-    mb_header* old = axl_get_mb_header(ptr);
+    mb_header* old = axl_ptr_to_mb(ptr);
     if(axl_split_mb(old, size))
     {
         return ptr;
@@ -217,9 +245,9 @@ void axl_free(void* ptr)
         return;
     }
 
-    mb_header* block = axl_get_mb_header(ptr);
+    mb_header* block = axl_ptr_to_mb(ptr);
-    mb_header* next_block = block->next;
+    mb_header* next_block = axl_id_to_mb(block->next);
-    mb_header* prev_block = block->prev;
+    mb_header* prev_block = axl_id_to_mb(block->prev);
     block->is_free = true; 
 
     mb_header* free_block = block;
@@ -230,7 +258,7 @@ void axl_free(void* ptr)
         block->next = next_block->next;
         if(block->next)
         {
-            block->next->prev = block;
+            axl_id_to_mb(block->next)->prev = axl_ptr_to_id(block);
         }
     }
 
@@ -240,10 +268,10 @@ void axl_free(void* ptr)
         prev_block->next = block->next;
         if(prev_block->next)
         {
-            prev_block->next->prev = prev_block;
+            axl_id_to_mb(prev_block->next)->prev = axl_ptr_to_id(prev_block);
         }
         free_block = prev_block;
     }
     
-    nomad = free_block;
+    nomad_handle = axl_ptr_to_id(free_block);
 }